A sample of compound X is found to contain 12.3 g of O, 18.4 g of C, and 25.7 g of N. The Law of Definite Proportion says if it weighs 90.3 g, how many grams of carbon are there?

1 Answer
Oct 9, 2017


There are 29.5 g of carbon.


The mass of the first sample is the sum of the masses of its elements.

#"Mass of sample" = "(12.3 + 18.4 + 25.7) g" = "56.4 g"#

According to the Law of Definite Proportions, every sample of #"X"# will contain 18.4 g of #"C"# in 56.4 g of #"X"#.

Thus, if you have a 90.3 g sample of #"X"#,

#"Mass of C" = 90.3 color(red)(cancel(color(black)("g X"))) × "18.4 g C"/(56.4 color(red)(cancel(color(black)("g X")))) = "29.5 g C"#